1. Field of the Invention
The present invention relates generally to optical fiber systems and, more particularly, to systems and methods that detect a potentially dangerous condition in an optical system and take precautionary measures to reduce or eliminate the potentially dangerous condition. The present invention also relates to systems and methods that detect signal and pump path integrity.
2. Description of Related Art
Optical communication systems have replaced other communication mediums due to their many advantages. For example, optical communication systems typically have wide bandwidth and low attenuation, are immune to electrical noise, offer relatively secure transmission of signals, and can transmit signals over long distances.
Despite the low attenuation of optical communication systems, the optical signals they transmit nevertheless require amplification. Although many types of optical amplifiers currently exist, the most widely used amplifiers are lumped or discrete amplifiers. Discrete amplifiers typically include an optical fiber doped with an optically active material, such as erbium or other rare earth elements. Generally, the core region of the optical fiber contains the dopant, which is optically excited to provide optical gain to an optical signal having a suitable wavelength. The dopant may be excited by subjecting it to an optical pump signal of a suitable pump wavelength. For example, an erbium-doped fiber amplifier amplifies optical signals of wavelengths in the range of 1520 nm to 1580 nm when pumped by an optical pump signal of wavelength 980 nm or 1480 nm.
Other types of optical amplifier that are widely used in optical systems include distributed amplifiers which amplify a signal over a distributed segment of fiber. Examples of such distributed amplifiers include those based on stimulated Raman scattering or stimulated Brillouin scattering. Such amplifiers perform distributed amplification over a relatively long segment of fiber. A typical Raman amplifier may distribute amplification over 20 km of fiber.
Both discrete and distributed amplifiers typically use optical pump lasers to generate the pump signal. The lasers generate optical pump signals of high power density in the fiber, the connectors, and various other components of the optical system. This is particularly true of distributed amplifiers such as Raman amplifiers which may use such high power densities (e.g. 5 MW/cm2) that dangerous conditions exist when the pumping light escapes the optical system or when imperfect connections exist. Imperfect connections may be caused, for example, by imperfect mating of fibers or by surface contamination on the fiber ends (e.g. oils, dust, or dirt) that can absorb some of the optical pump power and cause a hot spot, which could irreparably damage the connector. Once damaged, the connector must be replaced.
Indeed, the high power density used by many optical pump lasers may exceed governmental safety standards. If the fiber or an optical component connected to the fiber is damaged in some way such as by cutting or breaking or if somebody disconnects a component downstream of the optical pump, then the pumping light may escape the optical system and thereby create a hazardous condition for humans. These hazardous conditions include not only risks of eye damage but also skin and perhaps even other bodily damage. A disconnected fiber end or a damaged fiber may also cause high power density pumping light to impinge on other optical components and cause damage.
Accordingly, there exists a need for a system which detects signal or pump path integrity of an optical system being pumped by optical amplifiers. A need also exists for a system that takes precautionary measures when the pumped optical fiber is damaged or when a connection or component in the optical system being pumped has failed or degraded.
Systems and methods consistent with the present invention address this need by monitoring back reflections of the pumping light that reflect off of imperfect connectors, damaged components, damaged fiber, etc to detect a potentially hazardous condition and take precautionary measures before significant damage can occur and before a hazardous condition exists.
In accordance with the purpose of the invention as embodied and broadly described herein, a system, in one implementation consistent with the present invention, prevents damage to at least one component of a laser apparatus including a pumping laser that emits a light signal of increasing power during power up. At least one component receives the pumping light signal from the laser, and reflects at least a portion of the pumping light signal when the component is faulty, damaged or imperfect. The system includes a detector and a monitoring circuit. The detector detects the reflected light signal; and the monitoring circuit receives the reflected light signal, determines an amount of power in the reflected light signal, calculates a ratio of the power of the light signal emitted by the laser to the power in the reflected light signal, compares the ratio to a predetermined threshold to determine whether the imperfect connection or damaged component exists, sends a notification to an operator and/or shuts down the laser when the faulty or damaged component exists.
In another implementation consistent with the present invention, a system detects an imperfect connection in a laser component. The system includes a laser, a connector, and a monitoring circuit. The laser emits a light signal; the connector transmits the light signal external to the laser component and reflects at least a portion of the light signal when an imperfect connection exists; and the monitoring circuit detects an amount of the reflected light signal and determines that the imperfect connection exists when the detected amount of the reflected light signal exceeds a predetermined amount.
In yet another implementation consistent with the present invention, an optical amplifier includes an active optical fiber and at least one laser component. The laser component provides power to the active optical fiber. The laser component includes a laser, a connector, and a monitoring circuit. The laser outputs a light signal. The connector transmits the light signal to the active optical fiber and reflects at least a portion of the light signal when an imperfect connection exists. The monitoring circuit determines whether the imperfect connection exists using the reflected light signal.
In yet another implementation consistent with the present invention, an optical amplifier such as a Raman or Brillouin amplifier includes an optical pumping source connected to a fiber optic system and pumping the optical fiber at a wavelength selected to provide gain to a signal travelling in a segment of the optical fiber. If the optical fiber is damaged or if a connection or component in the optical system is degraded or failed, then these conditions cause pumping light to be reflected. A back reflection detector detects the amount of the reflected light signal and a controller takes at least one precautionary measure when the detected amount of the reflected light signal exceeds a threshold value. The at least one precautionary measure includes shutting down or reducing output power of the optical pump source.
In still another implementation, the controller may compare the detected amount of reflected light against two or more thresholds. Exceeding the first threshold may indicate a degraded condition while exceeding the second threshold may indicate a failed condition. The controller may then use these thresholds to decide between shutting down and reducing output power of the optical pump. Exceeding the first threshold may also indicate that the condition may be continuing to degrade and maintenance is required before the second threshold is reached.
In yet another implementation, a switchable attenuator, located between the optical pump and the optical system, may be controlled to attenuate the pumping light or prevent it from entering the optical system.
Another precautionary measure that may be used by the invention is the setting a maintenance flag, raising of an alarm or otherwise notifying personnel of a problem. Such flags and alarms can notify maintenance crews of the hazardous condition so that they can protect themselves as well as begin fixing the degraded condition that caused the back reflection before damage or hazardous conditions occur.
In yet another implementation in which a plurality of optical pump sources are utilized to amplify the signal, the invention may detect a backreflection from one optical pump source and control all of the optical pump sources to reduce power or shut down.
The systems and methods of the invention may operate during power up such that detection of back reflections and the taking of precautionary measures may occur while the optical pump source emits the pumping light signal with increasing power during a power up sequence. The invention may also be continuously operable during power up and steady state operational modes.
The amount of detected back reflection may be quantified in various ways including the power or energy received by a photodetector. Any such quantifications may be compared against one or more thresholds to determine a degraded or failed condition.
The inventive methods also include detecting signal or pump path integrity in a fiber optic system including an optical fiber and an optical pump source. To detect signal or pump path integrity the inventive methods provide gain to a signal travelling in a segment of the optical fiber with the optical pump source; detect a reflected light signal, wherein the reflected light signal is a reflected pumping light signal from the optical pump source that is reflected when the optical fiber is damaged or when a connection or component in the optical system is degraded or failed; and determine that the signal path integrity is compromised when a detected amount of the reflected pumping light signal detected by said detecting step exceeds a threshold value. As above, the threshold may include a plurality of thresholds to distinguish between, for example a failed state and a degraded state
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.